Re: [PATCH] linux-user: Drop unnecessary check in signalfd4 syscall

[Laurent Vivier <laurent@vivier.eu>]

Le 24/04/2020 à 23:04, Helge Deller a écrit :
> The signalfd4() syscall takes optional O_NONBLOCK and O_CLOEXEC fcntl
> flags.  If the user gave any other invalid flags, the host syscall will
> return correct error codes, so simply drop the extra check here.
> 
> Signed-off-by: Helge Deller <deller@gmx.de>
> 
> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
> index 05f03919ff..ebf0d38321 100644
> --- a/linux-user/syscall.c
> +++ b/linux-user/syscall.c
> @@ -7176,9 +7176,6 @@ static abi_long do_signalfd4(int fd, abi_long mask, int flags)
>      sigset_t host_mask;
>      abi_long ret;
> 
> -    if (flags & ~(TARGET_O_NONBLOCK | TARGET_O_CLOEXEC)) {
> -        return -TARGET_EINVAL;
> -    }
>      if (!lock_user_struct(VERIFY_READ, target_mask, mask, 1)) {
>          return -TARGET_EFAULT;
>      }
> 

Perhaps we want to trigger the TARGET_EINVAL before the TARGET_EFAULT if
we have both cases?

But I've checked the kernel, and the kernel does a copy_from_user()
before checking the flags, but it returns EINVAL rather than EFAULT.

We can remove the flags checking but we should also change TARGET_EFAULT
by TARGET_EINVAL.

Thanks,
Laurent